# Copyright 2014-2016 OpenMarket Ltd
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.

import logging
import re
from typing import TYPE_CHECKING, Optional, Tuple

from signedjson.sign import sign_json
from unpaddedbase64 import encode_base64

from twisted.web.server import Request

from synapse.http.servlet import RestServlet
from synapse.types import JsonDict

if TYPE_CHECKING:
    from synapse.server import HomeServer

logger = logging.getLogger(__name__)


class LocalKey(RestServlet):
    """HTTP resource containing encoding the TLS X.509 certificate and NACL
    signature verification keys for this server::

        GET /_matrix/key/v2/server HTTP/1.1

        GET /_matrix/key/v2/server/a.key.id HTTP/1.1

        HTTP/1.1 200 OK
        Content-Type: application/json
        {
            "valid_until_ts": # integer posix timestamp when this result expires.
            "server_name": "this.server.example.com"
            "verify_keys": {
                "algorithm:version": {
                    "key": # base64 encoded NACL verification key.
                }
            },
            "old_verify_keys": {
                "algorithm:version": {
                    "expired_ts": # integer posix timestamp when the key expired.
                    "key": # base64 encoded NACL verification key.
                }
            },
            "signatures": {
                "this.server.example.com": {
                   "algorithm:version": # NACL signature for this server
                }
            }
        }
    """

    PATTERNS = (re.compile("^/_matrix/key/v2/server(/(?P<key_id>[^/]*))?$"),)

    def __init__(self, hs: "HomeServer"):
        self.config = hs.config
        self.clock = hs.get_clock()
        self.update_response_body(self.clock.time_msec())

    def update_response_body(self, time_now_msec: int) -> None:
        refresh_interval = self.config.key.key_refresh_interval
        self.valid_until_ts = int(time_now_msec + refresh_interval)
        self.response_body = self.response_json_object()

    def response_json_object(self) -> JsonDict:
        verify_keys = {}
        for signing_key in self.config.key.signing_key:
            verify_key_bytes = signing_key.verify_key.encode()
            key_id = "%s:%s" % (signing_key.alg, signing_key.version)
            verify_keys[key_id] = {"key": encode_base64(verify_key_bytes)}

        old_verify_keys = {}
        for key_id, old_signing_key in self.config.key.old_signing_keys.items():
            verify_key_bytes = old_signing_key.encode()
            old_verify_keys[key_id] = {
                "key": encode_base64(verify_key_bytes),
                "expired_ts": old_signing_key.expired,
            }

        json_object = {
            "valid_until_ts": self.valid_until_ts,
            "server_name": self.config.server.server_name,
            "verify_keys": verify_keys,
            "old_verify_keys": old_verify_keys,
        }
        for key in self.config.key.signing_key:
            json_object = sign_json(json_object, self.config.server.server_name, key)
        return json_object

    def on_GET(
        self, request: Request, key_id: Optional[str] = None
    ) -> Tuple[int, JsonDict]:
        # Matrix 1.6 drops support for passing the key_id, this is incompatible
        # with earlier versions and is allowed in order to support both.
        # A warning is issued to help determine when it is safe to drop this.
        if key_id:
            logger.warning(
                "Request for local server key with deprecated key ID (logging to determine usage level for future removal): %s",
                key_id,
            )

        time_now = self.clock.time_msec()
        # Update the expiry time if less than half the interval remains.
        if time_now + self.config.key.key_refresh_interval / 2 > self.valid_until_ts:
            self.update_response_body(time_now)
        return 200, self.response_body
